Temperature regulated electronic apparatus



1944- G. GRAVESON ET AL 2,364,136

TEMPERATURE REGULATED ELECTRONIC APPARATUS File'd Dec. 31, 1942 /4 TUNED T0 REC-T/F/ER VOLTAGE AC. POWER SUPPLY ATTORNEY mean Dec. 5, 1944 TEMPERATURE REGULATED ELECTRONIC v APPARATUS George L. Graveson, Amltyville, N. Y., and Clyde It. Keith, Maplewood, N. J.,

assignors to Western Electric Company, Incorporated, New York, N. Y., a corporation of New Yorlr Application December 31, 1942, Serial No. 470,744 7 Claims. (01. 179-111) This invention relates to electronic apparatus, and more particularly to temperature regulated electronic apparatus. 1

In certain circuits of the prior art, such as crystal controlled diathermy circuits, a source of alternating current of a certain'individual frequency is applied to a load circuit tuned to the certain individual frequency. Usually, these circuits embody power amplifier apparatus comprising a pair of electronic devices arranged in push-pull relation such that their anodes are energized by rectified voltage supplied by suit- .able electronic rectifying apparatus. In the operation of the foregoing circuits, it may happen that a change in the relative positions of the diathermy electrodes would tend to detune the load circuit. In case of such happening, the amplifier devices would tend to draw an amount of anode current which would generate such amount of heat as would tend to damage the amplifier devices. The replacement of damaged electronic devices would tend to multiply unnecessarily the cost of operating the circuits;-' and incases where such replacements were not readily obtainable, the circuits would be rendered useless for indeterminate periods of time thereby increasing further the cost of operating the circuits.

A high frequency power amplifier operating at high efficiency (class C) should be protected from damage to the vacuum tubes which (damage) may result from any one of several conditions, such as too-low load resistance, detuning of plate coupling, failure of excitation, and open grid bias resistor. A common form of protecode circuit, but this reduces the efiiciency for normal operation and does not limit the plate current sufiiciently to prevent a considerable increase in heating under abnormal conditions. A relay arranged to cut oil the plate voltage if the grid current falls below a predetermined minimum protects against failure of grid excitation, but not for abnormal load conditions. A relay arranged to cut oil the plate voltage when the plate current exceeds a predetermined amount completely stops the circuit from operating even with a small overload. The method .tion is the use of a biasing resistor in the cathof protection which is the subject of this inve'ntion protects against all abnormal conditions without interrupting operation of the circuit, merely limiting the'applied plate voltage to an amount which isvsafe for the conditions then existing.

The present invention contemplates, an auto- 65 the power amplifier devices. The heat gener-' matic arrangement for preventing the fiow of an injurious amount of anode current in electronic apparatus.

The main object of the invention is to control the maximum amount of heat generated by the anode current flowing in electronic apparatus.

Another object is to control the rectified voltage supplied to the anodes of electronic apparatus. 7

A further object isto control the anode current flowing in electronic apparatus.

In the prior art circuits of the type above referred to, a source of alternating current of a certain frequency i1 is applied to the input circuit of power amplifying apparatus comprising a pair of three-element electronic devices arranged in push-pull to amplify the current of the certain frequency f1 such that both the input and output circuits of this apparatus are tuned to' the certain frequency f1. Jhe output circuit of this amplifying apparatus is applied to a load circuit which is also tuned to the certain frequency h. The anode circuits of such amplifying electronic devices may be energized by rectified voltage supplied thereto .by a pair of further three-element electronic devices opcrating from commercial source of alternating cluded in one arm of the phase-shifting bridge.

The temperature of the thermoresponsive element and thereby the effective resistance thereof is controlled 'by the heat generated by the anode current flowing in the power amplifier devices. The thermoresponsive element may be mounted in a tubular shield which tends to concentrate on the thermoresponsive element, the heat generated by such anodes, and which at the same time tends to minimize the eflect of radiant heat from sources other than such anodes.

In operation, the phase-shifting bridge is initially adjusted by means of a variable resistance connected in shunt of the thermoresponsive element such that a predetermined magnitude of rectified voltage is supplied to the anodes, of

paratus utilized in Figs. 1 and 3.

ated by the anode current in these devices serves to provide the thermoresponsive element with a predetermined temperature and thereby a predetermined effective resistance. This means that acertain phase relation is established between relative impedances of the-arms of the phaseshifting bridge are altered so that the phase of the potential on the control grids of the rectifying devices with respect to the phase of the potential on the associated anodes is varied in such manner as to reduce the magnitude of the rectified voltage supplied to the anodes of the power amplifier devices. This tends to cause the anode current in the power amplifier devices to be reduced thereby reducing the heat generated in the anodes thereof. As a consequence of its rapid change of resistance with temperature, the temperature/of the thermoresponsive element needs to rise only a very small amount to reduce the plate voltage to a degree such that the anode heating is allowed to increase only by a correspondingly small amount. The result is that the anode temperature rises only slightly above that occurring for normal operation.

\ A feature of the invention is that the control of the temperature of the power amplifier devices may be substantially improved by inserting a further 'thermoresponsive element provid- -ed with another preselected temperature coefiicient of resistance in a second arm of the phaseshifting bridge. In this feature, the two. individual thermoresponsiv elements are disposed adjacent each other and intermediate both power amplifier devices and simultaneously vary' their effective resistances in an opposite sense.

I A further feature is that additional sensitivity may be obtained by connecting one or more similar thermoresponsive elements in series and/or 4 parallel with eachof the thermoresponsive elements individual to the two arms of the phaseshifting bridge.

The invention will be readily understood from essence transformer it to a load l5 tuned by the secondary winding of the "latter transformer and capacitor l6 to the alternating current of the certain frequency Ii. The capacitors l1 and I8 neutralize the grid-to-plate capacitances of the power devices l2 and I3 so that they will not oscillate by themselves. The double capacitor it together with the split primary windings of the output transformer l4 serve to tune the output circuit of the push-pull devices l2 and I3 to the alternating current of the certain frequency ii. In the case of diathermy apparatus, the load I5 is replaced by the usual diathermy electrodes, not shown. A resistor 20 serves to apply negative bias to the control grids of the .power devices i2 and It.

The anodes of the power devices I2 and is are supplied with rectified voltage from the electronic voltage rectifier 25 in a manner that will now be explained. A supply 26 of commercial alternating current is coupled by primary winding 27 and split secondary winding 28 of a transformer 29 to the anodes 30 and 3| of a pair of .rectifying electronic devices 32 and 33, respectively. The control grids 34 and 35 of the latter devices are applied to split secondary winding 33 of a transformer 31 whose primary windin 38 is connected across the vertical diagonal of a. phase-shifting Wheatstone bridge 39. The horizontal diagonal of this bridgeis connected via leads 40 and 4| across the supply 26.

The other secondary windings 42 and 43 are understood to be connected over leads, not shown, to the filaments F1 and F: of the pairs of power devices l2 and I3 and rectifying devices 32 and 33, respectively. A lead 44 connects the midthe following description taken together with the accompanying drawing, in which: Fig. 1 is a diagrammatic circuit showing an electronic apparatus regulated from the standpoint of temperature in accordance with a specific embodiment of the invention;

Fig. 2 is a partial schematic view of the apparatus utilized in Fig. 2;

Fig. 3 is'a partial diagrammatic circuit of a modification that may be embodied in Fig. 1;

Fig. 4 is a partial schematic view of the ap- In the drawing the same reference numerals are employed to designate the same elements appoint of the split secondary winding 33 of the transformer 31 to the midpoint of the split primary winding of the output transformer l4 and '40 thereby to the anodes of both devices i2 and It.

A lead 45 connects the midpoint of the split secondary winding 28 of the transformer 29 to one side of the other secondary winding 42 of the latter transformer.

In the operation of Fig. 1, the source l0 supplies alternating current of certain frequency ii to the power amplifier comprising devices 12 and 13 whose output supplies amplified current of the certain frequency h to the load circuit l5 arranged to utilize amplified current of such frequency. To activate the power devices I2 and I3 for this'purpose, the rectifying devices 32 and 33, which'are preferablyof the gas-filled type, operate as a full-wave rectifier to supply rectified voltage to the anodes of the power devices I! and 13. This rectified voltage is effective over a circuit comprising control grid-cathode circuits of the rectifying devices 32 and 33, lead 44, midpoint of the split primary winding of the output transformer l4, anode-cathode circuits of the power devices I2 and I3, secondary winding 42 of the transformer 23, and lead 45 connected effectively to the midpoint of the split secondary wind-,

ing 28 applied to the anode circuits of therectifying devices 32 and 3.3. i

magnitudepfthe rectified voltage supplied to the anodes of the power devices l2 and II by the rectifying devices 32 and 33 is determined by the phase of the'potentialon the control grids The in shunt oi' the capacity arm Ii of the phaseshiiting bridge 3! enables adjustment. of the bai- I ance of the latter such that a predetermined phase relation is initially established between the potentials on the anodes 30 and ii, and control grids 34 and 35. This causes the magnitude or the rectified voltage applied to the anodes of the power devices I! and I3 in the manner above efiilained to be initially set at'a predetermined v ue.

.The foregoing describes a circuit and operation, both or which are known in the prior art; However, in the operation of such circuit it may happen that the load circuit i tends to become detuned, for the reason hereinbefore mentioned, with respect to the current of the certain irequency 11 being supplied by the output circuit of the power devices I2 and 13. As a consequence of such detuning, the power devices l2 and II tend to draw an increased amount of anode current which does not reach the load circuit II but flows only in the output circuit of the power devices I2 and i3. Such increasedamount of an- I ode current tends to generate heat in the anodes oi the power devices l2 and II which heat, it unchecked, will tend to cause damage to the latter devices. The heat generated by such power consumption by the anodes of the power devices I! and I3 will tend to cause their breakdown and thereby to shorten their useful life.

In accordance with the specific embodiment of the invention shown in Figs. 1 and 2, an automatic arrangement "is provided for limiting the maximum amount of power which may be consumed by the anodes of the power devices I! and II. This is accomplished by utilizing the heat radiated by the anodes of both power devices I2 and ll in a mannerthat will now be explained. A

thermoresponsive element 55 provided with a preselected temperature coeflicient oi resistance is disposed substantially intermediate the anodes oi the power devices l2 and I3, Fig. 2, and connected by leads 58 and 51 to the-capacity arm H of the phase-shifting bridge 38. The thermoresponsive element 55 may be of the disc type disclosed in the patent of W. F. Janssen No. 2,219,365, issued October 29, 1940, and provided with a negative temperature ooefiicient of resistance. The thermoresponsive element 55 may be mounted in a tubular heat shield 58, Fig. 2, which tendato 'concentrate on the former element the heat generated by both anodes of the power devices I! and II, and at the same time to minimize on the thermoresponsive element 85 the effect of heat generated bysources, not shown, other than the anodes'oi both power devices I! and II.

When theanodes oi the power devices I! and II tend to draw an excessive amount of space current for the reason mentioned previously, the heat generated by the anodes of both power devices I I and i3 and radiated thereby causes the ther-.

moresponsive element 55 to increase its temperature to a corresponding extent. -This causes a certain reduction in the eiiective resistance oi the thermoresponsive element II and thereby a certain change in the effective impedance of the capacity arm Si or the phase-shifting bridge 3!. This causes the phase of the potential on the control grids 34 and 35 of the rectiiying devices I! and "to vary with respect to the phase of the potential onthe anodes and II or both latter devices. This causes the magnitude of the rectified voltage suppli d to the anodes of the power devices it and II to reduce to such precludes damage to either one or both latter demain response to the heat generated in either one or both anodes oi the power devices I! and II Thus, the thermoresponsive element 55 serves to prevent the generation of excessive heat in the anodes of both power devices I! and I3, and thereby precludes damage to either one or both latter devices irom such heat. As the temperature of the anodes of the power devices I! and i3 is restored to a normal value, the thermoresponsive element 58 functions in an opposite sense to restore the predetermined magnitude of rectified voltage to the anodes of both power devices l2 and IQ for their normal operation. The arrangement illustrated in Figs. 1 and 2 may be further improved by connecting several of the thermoresponsive elements 55 -in series and/or parallel, in order to operate in the range of resistance variation most suitable for the particular circuit. Fig. 3 shows a modification for effecting an increase in the sensitivity of the circuit of Fig. 1. In this connection it is understood that the circuit portion shown in Fig. 3 is substituted for the circuit portion shown to the right or the line X-X in Fig. 1. Referring to Fig. 3, a thermoresponsive element 80 is also disposed intermediate the power devices I! and I3, Fig. 4, and connected via leads BI and 02 in shunt of capacity arm 83 of the phase-shifting bridge 39. The

thermoresponsive lement 60 may be of the disc type disclosed in the patent of G. L. Pearson, No. 2,258,958, issued October 14, 1941, and provided with a positive temperature coefiicient of resistance. Thus, both thermoresponsive elements and are included within the heat shield 58, Fig. 4, so as to be subject to the same amount of heat generated by the anodes of both power devices 52 and II in the manner above explained. Variations in the eflective resistances of both thermoresponsive elements 55 and due to radiant heat from the anodes of both power devices i2 and I3 cause both capacity arms ii and 63 01 the phase-shifting bridge 38 to vary their effective impedances in an opposite sense.

Hence, the adjustment of the unbalance oi the in the case or the thermoresponsive element ll in Fig. 1, the operating range of the circuit combination of Figs. 1 and 3 may be further improved by connecting several of the thermoresponsive elements 60 in series and/or parallel.

What is claimed is:. 1

1. In combination in tem rature controlled electronic apparatus comprising a load circuit, means including electronic apparatus to supply electrical energy to said load circuit such that the temperature 0! said electronic'apparatus is energy consumed therein, means comprising a 5 thermoresponsive element having a' preselected temperature coemcient of resistance and disposed in proximity f said electronic apparatus to control the operation of said energizing control means in response to temperature variations of said electronic apparatus.

. 2..In combination in temperature controlled electronic apparatus comprising a load circuit, means including electronic apparatus to supply electrical energy to said load-circuit such that the temperature of said electronic apparatus is caused to vary'in response to the amount of the space current flowing therein, and means to activate said electronic apparatus for effecting the flow of space current therein including a Wheatstone bridge whose condition of unbalance determines the amount of the activation of said electronic apparatus and thereby the temperature thereof, means comprising a thermoresponsive element having a preselected temperature coeflicient of resistance and included in one arm of said bridge and disposed in proximity of said electronic apparatus to vary the condition of un-' balance of said bridge in response to the temperature variations of said electronic apparatus.

3. In combination in temperature regulated I electronic apparatus, a load circuit, means to supply electrical energy to said load circuit including a pair of electronic devices arranged in push-pull relation, each of said devices including an anode supply impressed on said control grids whereby,

which is subject tovariations in temperature as the amount of electricalenergy consumed thereby undergoes changes, means to energize said anodes, and means comprising a thermoresponsiveelement havinga preselected temperature coeflicient of resistance and disposed in proximity of said anodes to control the operation .of said energizing means and thereby the amount oi electrical energy consumed by said anodes as variationsoccur in the temperature of said anodes.

4. In combination in temperature regulated electronic apparatus comprising; a load circuit, means to supply electrical energy to said load circuit including at least two electronic devices,

each including an anode whose temperature varies as changes occur in the amount of electrical energy consumed thereby, and means to utilize the phase relation between two different portions of further electrical energy to activate said anodes, means comprising a thermoresponsive element having a preselected temperature coeflicient of resistance and disposed in proximity of said anodes to vary the phase of one of said two difierent portions of said further electrical energy in response to the tions of said anodes.

5. A temperature controlled electronic appatemperature variaratus comprising a source of electrical waves,

means comprising electronic apparatus to amplify tosupply voltage to said electronic apparatus to 7 activate the flow of space current'thereinineluding a Wheatstone bridge whose condition-of 1 unbalance determines the amount otactivation oisaid electronic apparatus and thereby the temperature thereof, and means comprising a pair of thermoresponsive elements having preselected opposite temperature coeflicients of resistance and individually included in one of two arms of said bridge and disposed in proximity of said electronic apparatus to vary the condition of unbalance of said bridge in response to temperature variations of said electronic apparatus.

6. A temperature regulated electronic apparatus comprising a source of electrical waves, means to amplify said electrical waves comprising one pair of'electronic devices arranged-in pushpull relation, each of said one pair of devices including an anode,.the anodes of said one pair of devices varying in temperature in proportion to the amount of space current flowing therein, a load circuit to utilize the amplified electrical waves, and means to supply rectified voltage 40 the anodes of said one pair of devices to control the amount oi'space current flowing therein. comprising a supply of alternating voltage, a further pair of electronic devices eachincluding 1 a control grid and an anode, said further devices being connected such thattheir anodes and control grids are applied to said supply, and a bridge interposed between said supply and the control grids of said further pair of devices to vary the phase of the portion of voltage supply impressed thereon whereby the magnitude of the rectified voltage is varied, and means comprising a thermoresponsive element having a preselected temperature coeflicient of resistance and included in one arm of said bridge and disposed in proximity to the anodes of saidone pair of devices to vary the phase of the portion of the voltage the magnitude of the rectified voltage supplied to said anodes of said one pair of devices is varied in response to the temperature variations of said anodes of said one pair of devices.

7. A temperature regulated electronic apparatus comprising a source of electrical waves, a load circuit, means comprising a pair of elec:

I tronic devices to amplify the electrical waves and .anodes of said amplifying devices varying their temperature as changes occur in the amount of .space current flowing in said latter devices,

means to supply rectified voltage to said anodes of said amplifying devices to control the amount of space-current fiowing therein, comprising a supply of alternating voltage, a pair of further electronic devices, each including a control grid and. an anode arranged such'that their anodes and control grids are connected to said supply,- a bridge interposedbetween said supply and said control grids of said further devices to vary the phase of the portion of the supply voltage applied thereto whereby the magnitude of the rectified voltage is controlled, and means comprising a pair of thermoresponsive elements having preselected opposite temperature coefilcients of resistance and included individually in one arm of said bridge and disposed in proximity of-said anodes of said amplifying devices to vary the phase of the portion of the voltage supplied to said control grids whereby the magnitude of rectifiedvoltage supplied to said anodes of said amplifying devices is varied in response to tem-- perature variations of said anodes oi said amplifying devices.

J GEORGE L. GRAVESON.

CLYDE R. KEITH. Y 

